1. Field of the Invention
The present invention relates to an angle information input apparatus for inputting angle information by designating at least two positions in relation to a coordinate input tablet.
2. Description of the Related Art
FIGS. 1A and 1B are respectively a plan view and a sectional view of a known angle information input apparatus. The input apparatus is formed, as illustrated in FIGS. 1A and 1B, in a cylindrical shape having a predetermined height. The apparatus is formed of a main unit 10 having a hollowed-out center and a rotator 20. The rotator 20 fits completely in the hollowed center of the main unit 10 and is smoothly rotated therein without any play by application of a force. The main unit 10 has a bottom surface, and the rotator 20 is thus prevented from dropping even if the main unit 10 is lifted.
The main unit 10 and the rotator 20 are concentrically formed around the center axis O, and the rotator 20 is rotated around the center axis O within the main unit 10 by inserting a finger into a disc-like indentation 30 that is formed on the upper surface of the rotator 20 and by orbiting the indentation 30.
Provided at the center bottom of the main unit 10 is a first position-designating portion (tuning circuit) 40 of a first tuning frequency f1, which is formed of a circular coil and a capacitor and the center of which matches the center axis O. Only the position of the coil is shown by the dotted circle. The center point of the coil, i.e., the intersection between the center axis O and the bottom of the main unit 10 is indicated by O'.
Provided at the bottom of the rotator 20 is a second position-designating portion (tuning circuit) 50 of a second tuning frequency f2 (f2 is not equal to f1), which is formed of a circular coil and a capacitor. The second position-designating portion 50 is displaced from the rotating axis of the rotator 20, i.e., from the center axis O. This displacement prevents the first and second position-designating portions 40 and 50 from overlapping with each other in any situation under which the rotator 20 is rotated. The second position-designating portion 50 orbits around the first position-designating portion 40 in such a manner that it moves on a circular arc having a predetermined radius.
A tablet used with this known input apparatus is of the type which is able to detect the positions designated by at least the first and second position-designating portions (having the different tuning frequencies f1 and f2) 40 and 50. Such a tablet is already known and an explanation thereof is thus omitted. A method for inputting angle information into a host computer (more precisely, application software) by using the above type of tablet is, for example, as follows.
FIG. 2 illustrates the first and second position-designating portions 40 and 50 located on the input area of the tablet, the lower left corner of which is determined to be the origin (O, O). The positions (X.sub.1, Y.sub.1) and (X.sub.2, Y.sub.2) respectively designated by the first and second position-designating portions 40 and 50 detected by the tablet are input via a predetermined interface into a tablet driver (software) installed in the computer. The tablet driver then calculates the following angle according to the foregoing two positions (coordinates), ##EQU1## and sends the calculated angle to the application software. Then, the application software is run based on the angle information received from the tablet driver (see FIGS. 2 and 3). It is now assumed that the second position-designating portion 50 orbits around the first position-designating portion 40 by rotating the rotator 20, as shown in FIG. 4, from the original position indicated by the dotted circle to the position represented by the solid circle. The angle .alpha..sub.1 is the angle between the horizontal line and the line joining the original position of the second position-designating portion 50 with the first position-designating portion 40, and the angle .alpha..sub.2 is the angle between the horizontal line and the line joining the new position of the second position-designating portion 50 with the first position-designating portion 40. According to the above equation, angles .alpha..sub.1 and .alpha..sub.2 may be separately input as absolute angles into the application software. Alternatively, a change .DELTA..theta. in the angle .alpha..sub.2 -.alpha..sub.1 obtained by moving the second position-designating portion 50 may be input.
The input apparatus is adapted to input the angle information while being placed on the input area of the tablet. Accordingly, the tablet driver calculates the angle only from the positions designated by the two position designating-portions 40 and 50 which are located on the tablet. Thus, disadvantageously, angle information may be input into the tablet driver even when the input apparatus itself is moved on the tablet rather than the rotator 20. This is explained in detail below with reference to FIG. 5.
It is now assumed that the first position-designating portion 40 is shifted, as shown in FIG. 5, from the position indicated by the dotted circle to the position indicated by the solid circle, by moving the input apparatus located on the input area of the tablet. The angle of the second position-designating portion 50 in relation to the center of the first designating-portion 40 prior to the shifting is indicated by .alpha..sub.1, while the angle of the second position-designating portion 50 in relation to the center of the first designating-portion 40 subsequent to the shifting is represented by .alpha..sub.2. Then, the driver tablet inputs these angles .alpha..sub.1 and .alpha..sub.2 as absolute angles or as a change in the angle .alpha..sub.2 -.alpha..sub.1 into the application software even though the second position-designating portion 50 (the rotator 20) has not orbited.
One method to overcome the above drawback may be to constantly monitor a change in the position of the first position-designating portion 40 by the tablet driver and to prevent the input of the angle information obtained when the first position-designating portion 40 moves. However, this does not satisfy the need in which the input apparatus is moved to a given position on the tablet to input angle information.